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Novel Syntheses, Structures and Functions of Mesoporous Silica Materials
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Nanoteknologi och funktionella material. (Nanoteknologi och funktionella material)
2010 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

The field of mesoporous silica has been studied for about 20 years but it is still an area attracting a lot of attention. The use of novel templating molecules and several issues related to the synthesis and fine structural details are still poorly understood. These aspects are of special relevance to the theme of this thesis, which includes novel work on three fronts; the synthesis, characterization and applications of mesoporous materials.

The work described in this thesis aims to contribute to the mesoporous field by developing novel methods of mesoporous silica synthesis without relying on surfactant micelles as the templating agent but focusing instead on the stacking arrangement of aromatic molecules such as folic acid. The novel route presented here leads to 2D hexagonal structures with p6mm symmetry possessing high mesoporosity and large surface areas. The versatility of this route at various synthesis temperatures and using hydrothermal treatments has also been investigated.

A novel strategy is also proposed for the synthesis of mesocaged materials with Pm3n symmetry structures. The mechanism relies on the penetration of the neutral propylamino moiety of a co-structure directing agent into the hydrophobic core of the surfactant micelles. Beside these novel pathways, the effect of hydrothermal treatment (HT) at 100 oC on the 3D cubic Ia3d structure (AMS-6) over a long period of time was also examined, and the results show a phase transformation from a 3D cubic Ia3d to a 2D hexagonal p6mm structure and a return to the 3D cubic Ia3d structure at a later stage in the synthesis. This unexpected result is discussed.

In this work, the detailed structural characterization of mesoporous materials using electron microscopy techniques is an important task. In particular, to extend previous knowledge, the fine structural details of mesocaged materials possessing Pm3n symmetry prepared with various amphiphilic surfactants under acidic and alkaline conditions has been investigated using electron crystallography and sorption studies. The results show subtle fine structural differences with materials prepared under alkaline conditions exhibiting the largest mesocage sizes. The cage and window sizes are primarily determined by the charge density of the surfactant and the thickness of the hydration layer surrounding the surfactant micelles.

The relationship between the mesoporous structure and its function has been investigated by evaluating the rate of release of amphiphilic molecules, used as model molecules, from the internal pore structures of mesoporous materials with different pore geometries. In a similar study, the rate of proton diffusion from a liquid surrounding the mesoporous nanoparticles into the pore system of AMS-n was also assessed. The results show that the diffusion coefficients for the proton absorption process are higher than those for the release of the surfactant template molecules, with more complex 3D mesocaged particles showing the highest diffusion coefficients in both cases.

Finally, the quantity of CO2 adsorption was measured by modifying the internal surfaces of mesocaged material with n-propylamino groups. Results show that the cage-connecting window sizes limit the surface coverage of n-propylamino groups by pore blocking and affect the volume of CO2 adsorption. In addition, at the molecular level, CO2 adsorption shows physisorption or chemisorption depending on the localized distribution of n-propylamino groups, as studied by in-situ infrared spectroscopy.

sted, utgiver, år, opplag, sider
Uppsala: Acta Universitatis Upsaliensis , 2010. , s. 82
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 733
HSV kategori
Forskningsprogram
Materialvetenskap
Identifikatorer
URN: urn:nbn:se:uu:diva-122289ISBN: 978-91-554-7786-8 (tryckt)OAI: oai:DiVA.org:uu-122289DiVA, id: diva2:309625
Disputas
2010-05-21, Siegbahnsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:00 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2010-04-28 Laget: 2010-04-07 Sist oppdatert: 2010-05-18
Delarbeid
1. Structural variations in mesoporous materials with cubic Pm3n symmetry
Åpne denne publikasjonen i ny fane eller vindu >>Structural variations in mesoporous materials with cubic Pm3n symmetry
2010 (engelsk)Inngår i: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 133, nr 1-3, s. 27-35Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The fine structural details of mesoporous materials possessing Pm3n symmetry prepared with varying amphiphilic surfactants under acid and alkaline conditions are investigated using electron crystallography and sorption studies. The structural data derived is used to understand the parameters that govern the formation of cavity-windows and to propose synthetic strategies in order to control independently the size of the cavities and cavity-windows. Results support that whilst attainment of Pm3n cubic packing is due to the overall surfactant geometry, the formation of cavity-windows is associated with the hydration layer formed at the interphase between the surfactant and the silica wall.  The charge density at the micelle surface may be tailored using two strategies: (i) using dicationic gemini surfactants at low pHs resulting in an increase in the hydration layer; or (ii) by using co-structure directing agents such as organoalkoxysilanes which reduce the hydration layer surrounding the micelles. The latter leads to the formation of higher cavity sizes and may be useful for tuning fine structural details of mesoporous materials when considering their use in important applications such as gas separation.

Emneord
Amphiphilic surfactants, Mesoporous materials, Electron microscopy, Structural solutions, Gas separation
HSV kategori
Forskningsprogram
Materialvetenskap
Identifikatorer
urn:nbn:se:uu:diva-121984 (URN)10.1016/j.micromeso.2010.04.007 (DOI)000279061000004 ()
Tilgjengelig fra: 2010-04-06 Laget: 2010-04-03 Sist oppdatert: 2017-12-12bibliografisk kontrollert
2. Nonsurfactant Supramolecular Synthesis of Ordered Mesoporous Silica
Åpne denne publikasjonen i ny fane eller vindu >>Nonsurfactant Supramolecular Synthesis of Ordered Mesoporous Silica
2009 (engelsk)Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, nr 9, s. 3189-3191Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Hoogsteen-bonded tetrads and pentamers are formed by a large variety of organic molecules through H-donor and acceptor groups capable of inducing self-organization to form columnar and hexagonal mesophases. The biological importance of such macromolecular structures is exemplified by the assembly of guanosine-rich groups of telomere units and their implication in chromosomal replication. Folic acid is composed of a pterin group, chemically and structurally similar to guanine, conjugated to an l-glutamate moiety via a p-amino benzoic acid. Our aim has been to develop a delivery vehicle for folic acid and at the same time provide a novel synthetic route for ordered mesoporous materials without the use of amphiphilic surfactants. We present a new nonsurfactant route for the synthesis of highly ordered mesoporous materials, based on the supramolecular templating of stacked arrays of the tetramer-forming pterin groups of folic acid under a variety of synthetic conditions. This method leads to hexagonally ordered mesoporous structures with gyroid, spherical, and chiral morphologies with pores on the order of 25−30 Å in diameter and surface areas above 1000 m2/g. More importantly circular dichroism studies reveal that the folate template possesses a chiral signature within the pores in the as-synthesized solid and that chirality is transferred from the folate template to the pore surface via the aminopropyl triethoxysilane costructure directing agent used in the supramolecular assembly. This novel templating approach for ordered mesoporous materials breaks the hegemony of surfactant micellar systems for the preparation of these exciting high surface area solids and opens new opportunities for structural control, design of pore geometry, and novel applications.

HSV kategori
Forskningsprogram
Teknisk fysik med inriktning mot nanoteknologi och funktionella material
Identifikatorer
urn:nbn:se:uu:diva-99093 (URN)10.1021/ja8096477 (DOI)000264792400033 ()19220057 (PubMedID)
Tilgjengelig fra: 2009-03-06 Laget: 2009-03-06 Sist oppdatert: 2017-12-13bibliografisk kontrollert
3. Hydrothermal Phase Transformation of Bicontinuous Cubic Mesoporous Material AMS-6
Åpne denne publikasjonen i ny fane eller vindu >>Hydrothermal Phase Transformation of Bicontinuous Cubic Mesoporous Material AMS-6
2008 (engelsk)Inngår i: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 20, nr 12, s. 3857-3866Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The controlled synthesis of ordered anionic surfactant templated mesoporous silica with cubic Ia3 structure (AMS-6) is reported via prolonged periods of hydrothermal treatment (HT). The cubic Ia3 mesophase transforms to hexagonal p6mm after 8 days of HT at 100 °C. Surprisingly, the hexagonal phase is stable only for a limited period after which a reversal to the cubic Ia3 mesostructure is observed. Characterization methods such as powder X-ray diffraction (XRD), electron microscopy (SEM, TEM), N2-isotherms, magic-angle spinning (MAS) 29Si NMR spectroscopy, and thermogravimetric analysis (TGA) have been employed to follow structural and textural changes of the materials prepared. Data show that the resultant mesostructure and its textural properties are highly dependent on the period of HT with less unit-cell shrinkage on calcination after extensive HT. Furthermore, evidence of two different solid−solid phase mechanisms during HT is presented. The initial transition is consistent with a restructuring of the surfactant packing and a depletion of the organic moieties from the organo-silica wall as evident from 29Si NMR spectroscopy. The return to the bicontinuous cubic phase is driven by changes in charge matching at the organic−inorganic interface as a result of increases in the polymerization of the silica wall. The textural properties, and in particular the presence or absence of surface porosity, has been controlled through variations in hydrothermal treatment. These are associated with specific growth directions of cubic AMS-6 crystals. The synthetic method described allows us to easily prepare phase pure and intermediate mesostructured nanoparticles.

HSV kategori
Forskningsprogram
Teknisk fysik med inriktning mot nanoteknologi och funktionella material
Identifikatorer
urn:nbn:se:uu:diva-98531 (URN)10.1021/cm702440n (DOI)000256854800015 ()
Tilgjengelig fra: 2009-02-25 Laget: 2009-02-25 Sist oppdatert: 2017-12-13bibliografisk kontrollert
4. Co-Structure Directing Agent Induced Phase Transformation of Mesoporous Materials
Åpne denne publikasjonen i ny fane eller vindu >>Co-Structure Directing Agent Induced Phase Transformation of Mesoporous Materials
2009 (engelsk)Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, nr 5, s. 3189-3195Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The synthesis of cubic Pmn mesocaged solid templated by cetyltrimethyl ammonium bromide (C16TMABr) surfactant by direct cocondensation of (3-aminopropyl)triethoxysilanes (APES) under strong alkaline conditions is reported. The novel route gives direct incorporation of amino functional groups on the porous silica wall, and the structural formation has been followed by means of in situ SAXS studies performed at a synchrotron beam line. Data shows that a molar ratio of C16TMABr/APES = 0.6 favors the formation of 3D cubic mesocaged solid with Pmn symmetry which transforms to a cylindrical mesoporous phase with p6mm symmetry at higher molar ratios. Further structural evaluation has been performed by means electron crystallography (EC). Reconstructed 3D models based on EC show the presence of spherical cages (A-cages, 45 Å) and ellipsoidal cages (B-cages, 48 × 43 Å) whereby every cage in the unit cell is connected to 14 nearest cages with a window size of 18 Å. Finally, a mechanism is proposed, denoted S+NoI, in which penetration of the neutral aminopropyl moiety within the micellar corona is responsible for the formation of the Pmn phase, accounting for the formation of the hexagonal phase at higher molar ratios and higher temperatures. In comparison to other mesocaged materials with the same symmetry this structure possesses a more open porous network which will help assess its potential in a variety of applications discussed herein.

HSV kategori
Forskningsprogram
Teknisk fysik med inriktning mot nanoteknologi och funktionella material
Identifikatorer
urn:nbn:se:uu:diva-99092 (URN)10.1021/la803727u (DOI)000263770800097 ()
Tilgjengelig fra: 2009-03-06 Laget: 2009-03-06 Sist oppdatert: 2017-12-13bibliografisk kontrollert
5. Temperature-Induced Uptake of CO2 and Formation of Carbamates in Mesocaged Silica Modified with n-Propylamines
Åpne denne publikasjonen i ny fane eller vindu >>Temperature-Induced Uptake of CO2 and Formation of Carbamates in Mesocaged Silica Modified with n-Propylamines
2010 (engelsk)Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, nr 12, s. 10013-10024Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Adsorption-mediated CO2 separation can reduce the costs of carbon capture and storage. The reduction in cost requires adsorbents with high capacities for CO2 sorption and high CO2-over-N2 selectivity. Amine-modified sorbents are promising candidates for carbon capture. To investigate the details of CO2 adsorption in such materials, we studied mesocaged (cubic, Pm3n symmetry) silica adsorbents with tethered propylamines using Fourier transform infrared (FTIR) spectroscopy and volumetric uptake experiments. The degree of heterogeneity in these coatings was varied by either co-synthesizing or post-synthetically introducing the propylamine modification. In situ FTIR spectroscopy revealed the presence of both physisorbed and chemisorbed CO2 in the materials. We present the first direct molecular evidence for physisorption using FTIR spectroscopy in mesoporous silica sorbents modified with propylamines. Physisorption reduced the CO2-over-N2 selectivity in amine-rich sorbents. Samples with homogenous coatings showed typical CO2 adsorption trends and large quantities of IR-observable physisorbed CO2. The uptake of CO2 in mesocaged materials with heterogeneous propylamine coatings was higher at high temperatures than at low temperatures. At higher temperatures and low pressures, the post-synthetically modified materials adsorbed more CO2 than did the extracted ones, even though the surface area after modification was clearly reduced and the coverage of primary amine groups was lower. The principal mode of CO2 uptake in post-synthetically modified mesoporous silica was chemisorption. The chemisorbed moieties were present mainly as carbamate–ammonium ion pairs, resulting from the quantitative transformation of primary amine groups during CO2 adsorption as established by NIR spectroscopy. The heterogeneity in the coatings promoted the formation of these ion pairs. The average propylamine–propylamine distance must be small to allow the formation of carbamate–propylammonium ion pairs.

Emneord
carbon dioxide, propylamine, adsorption, IR, FTIR, silica, mesoporous
HSV kategori
Forskningsprogram
Materialvetenskap
Identifikatorer
urn:nbn:se:uu:diva-121987 (URN)10.1021/la1001495 (DOI)000278427600114 ()
Tilgjengelig fra: 2010-04-06 Laget: 2010-04-03 Sist oppdatert: 2017-12-12bibliografisk kontrollert
6. Sustained Release from Mesosporous Nanoparticles: evaluation of structural properties associated with controlled release rate
Åpne denne publikasjonen i ny fane eller vindu >>Sustained Release from Mesosporous Nanoparticles: evaluation of structural properties associated with controlled release rate
2008 (engelsk)Inngår i: Current Drug Delivery, ISSN 1567-2018, E-ISSN 1875-5704, Vol. 5, nr 3, s. 177-185Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

We present here a detailed study of the controlled release of amino acid derived amphiphilic molecules from the internal pore structure of mesoporous nanoparticle drug delivery systems with different structural properties; namely cubic and hexagonal structures of various degrees of complexity. The internal pore surface of the nanomaterials presented has been functionalised with amine moieties through a one pot method. Release profiles obtained by Alternating Ionic Current measurements are interpreted in terms of specific structural and textural parameters of the porous nanoparticles such as pore geometry and connectivity. Results indicate that diffusion coefficients are lower by as much as four orders of magnitude in 2-dimensional structures in comparison to 3-dimensional mesoporous solids. A fast release in turn is observed from mesocaged materials AMS-9 and AMS-8 where the presence of structural defects is thought to lead to a slightly lower diffusion coefficient in the latter. Amount of pore wall functionalisation and number of binding sites on the model drug are found to have little effect on the drug release rate.

HSV kategori
Forskningsprogram
Teknisk fysik med inriktning mot nanoteknologi och funktionella material
Identifikatorer
urn:nbn:se:uu:diva-17498 (URN)10.2174/156720108784911686 (DOI)18673261 (PubMedID)
Tilgjengelig fra: 2008-08-07 Laget: 2008-08-07 Sist oppdatert: 2017-12-08bibliografisk kontrollert
7. Proton Absorption in As-Synthesized Mesoporous Silica Nanoparticles as a Structure-Function Relationship Probing Mechanism
Åpne denne publikasjonen i ny fane eller vindu >>Proton Absorption in As-Synthesized Mesoporous Silica Nanoparticles as a Structure-Function Relationship Probing Mechanism
Vise andre…
2009 (engelsk)Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, nr 8, s. 4306-4310Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

A new method to investigate the effect of pore geometry on diffusion processes in mesoporous silica nanoparticles and other types of micro- and mesoporous structures is put forward. The method is based onthe study of proton diffusion from a liquid surrounding the mesoporous particles into the particle pore system. The proton diffusion properties are assessed for a variety of as-synthesized mesoporous nano- and microparticles with two-dimensional and three-dimensional connectivity. Results show that the diffusion coefficients are higher for the proton absorption process than for the release of surfactant template molecules, and that they overall follow the same trend with the more complex three-dimensional mesocaged particles showing the highest diffusion coefficients. The pore geometry (cylindrical pores versus cage-type pores) and structure connectivity are found to play a key role for the effects observed. The results put forward in the present work should offer a valuable tool in the development of porous nanomaterials in a range of applications including the use as catalysis and separation enhancers in the petrochemical industry, as scaffolds for hydrogen storage, and as drug delivery vehicles for sustained release and gene transfection.

HSV kategori
Forskningsprogram
Teknisk fysik med inriktning mot nanoteknologi och funktionella material
Identifikatorer
urn:nbn:se:uu:diva-100974 (URN)10.1021/la900105u (DOI)000265281700015 ()19281159 (PubMedID)
Tilgjengelig fra: 2009-04-15 Laget: 2009-04-15 Sist oppdatert: 2017-12-13bibliografisk kontrollert

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